The invention relates to power-and-free conveyor systems of the type shown in U.S. Pat. No. 3,759,189, issued Sep. 18, 1973. The invention is particularly applicable to work carriers having front and rear trolleys constructed so as to permit close-packing or accumulation, and which pass through transfer points.
Among the problems with power-and-free systems is the danger of a carrier's inadvertently backing up. This can be overcome by the use of anti-backup means mounted on the carrier frame, such as disclosed in U.S. Pat. No.'s 3,159,189 and 3,354,834. However, those systems have slippage and, because they have cams which ride along the tracks, substantial wear of the anti-backup device occurs.